Every time edit and save order from Admin page it will email to customer, use extension "Optional Order Notifications" to close it when edit and save order - it works. But it also affect when customer checkout the order confirmation email also won't send to customer.

How it works with when customer checkout order will received order confirmation email - while at admin page edit and save order it unable send email to customer?

No OC version posted. However, since this issue is about an installed extension, contact the extension developer from where you originally downloaded extension in order to resolve this issue with the checkout email notifications.

The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.

Wonder it any other solution or at checkout.php put hidden notify column to make sure the email is send out when customer checkout?

Can you clarify what you mean by hidden more in details? Please explain the objective in details on what you are looking for to have.

The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.

OC ver 2.2.0.0 now working as:
Customer checkout => customer and admin received order confirmation email
Admin page edit and save order => customer and admin received order confirmation email

Currently only can works with extension:
Customer checkout => customer and admin won't received any order confirmation email
Admin page edit and save order => admin can choose yes or no to send order confirmation email

What I want for my website is:
Customer checkout => customer and admin received order confirmation email
Admin page edit and save order => admin can choose yes or no to send order confirmation email

Currently only can works with extension:
Customer checkout => customer and admin won't received any order confirmation email
Admin page edit and save order => admin can choose yes or no to send order confirmation email

Contact the extension developer to resolve this issue since the problem, according to your statement, is related with the extension.

The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.

This is a standard core function of Opencart, when you edit the order. What happens is actually, that you invalidate the old order and create a "new order" with the changed parameters. Since the API uses the catalog checkout process to create this new order, it automatically triggers the confirmation email.

Basically, that is standard business procedure to invalidate old order first, so that you can edit the order and create the same order with changed details. Nothing wrong with that, but the email however is a problem. There should be at least the option i the backend order edit if one wants to send the confirmation order or not.

From the admin order, where the comment is being entered, a notification email option should already be implicit. If not, on more recent OC versions, this option has definitely been added accordingly.

The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.